May 23, 2011: Though the universe is filled with billions upon billions of stars,
NASA's Hubble Space Telescope has been trained on a single variable
star that in 1923 altered the course of modern astronomy. And, at
least one famous astronomer of the time lamented that the discovery
had shattered his world view. The star goes by the inauspicious name
of Hubble variable number one, or V1, and resides two million
light-years away in the outer regions of the neighboring Andromeda
galaxy, or M31. V1 is a special class of pulsating star called a
Cepheid variable that can be used to make reliable measurements of
large cosmic distances. The star helped Edwin Hubble show that
Andromeda lies beyond our galaxy. Prior to the discovery of V1 many
astronomers, including Harlow Shapley, thought spiral nebulae,
such as Andromeda, were part of our Milky Way galaxy. Others
weren't so sure. In fact, Shapley and Heber Curtis held a public
debate in 1920 over the nature of these nebulae. But it took Edwin
Hubble's discovery just a few years later to settle the debate.
Hubble sent a letter, along with a light curve of V1, to Shapley
telling him of his discovery. After reading the note, Shapley
reportedly told a colleague, "here is the letter that destroyed
my universe." The universe became a much bigger place after Edwin
Hubble's discovery.

In commemoration of this landmark observation, astronomers with
the Space Telescope Science Institute's Hubble Heritage Project
partnered with the American Association of Variable Star Observers
(AAVSO) to study the star. AAVSO observers followed V1 for six
months, producing a plot, or light curve, of the rhythmic rise and
fall of the star's light. Based on this data, the Hubble Heritage
team scheduled Hubble telescope time to capture Wide Field Camera 3
images of the star at its dimmest and brightest light levels. The
observations are being presented on May 23 at the meeting of the
American Astronomical Society in Boston, Mass. Copies of the
photograph Edwin Hubble made in 1923 flew onboard space
shuttle Discovery in 1990 on the mission that deployed Hubble. Two
of the remaining five copies were part of space shuttle Atlantis's
cargo in 2009 for NASA's fifth servicing mission to Hubble. Edwin
Hubble's observations of V1 became the critical first step in
uncovering a larger, grander universe. He went on to measure the
distances to many galaxies beyond the Milky Way by finding Cepheid
variables within them. The velocities of those galaxies, in turn,
allowed him to determine that the universe is expanding. The space
telescope that bears his namesake continues using Cepheids to refine
the expansion rate of the universe and probe galaxies far beyond
Edwin Hubble's reach.